Sayuri was one of seven people killed in the deadliest fire in Massachusetts since 1994, a three-alarm inferno that devoured most of a sprawling apartment building that was home to more than 55 people.

Sayuri Sak was in a third-floor apartment with her family and died along with her parents, Torn Sak, his long-time partner, Ellen Vuong, and siblings Anthony, 12 and Ryan, 9. Two other siblings escaped.

Another victim of the fatal fire was identified by a relative as Tina Christakos, 38. Neighbors said the seventh victim was a man of about 70.

Lam’s mother, Susan Ngin, said she and her son was deeply moved when he learned that a friend of his had been lost in the fire.

“His face all of a sudden changed,’’ said Ngin, who lives nearby.

Ethen brought a book of poems that he and his classmates wrote, including one from his lost friend. Sayuri’s was entitled “My Puppy,” and it read in part: “My puppy is fun./ My puppy plays./ My puppy swims./ My puppy takes a shower./ My puppy likes me!”

Underneath the poem was a hand-drawn image that appeared to be a dog looking out a window.

Today, State Police assigned to State Fire Marshal Stephen D. Coan’s office, Lowell officials and agents from US Bureau of Alcohol,Tobacco, Firearms and Explosives were on the scene searching for the cause and origin of the fire. Because of the fatalities, Middlesex District Attorney Marian T. Ryan’s office is overseeing the investigation.

In a statement released late this afternoon, Ryan’s office said the cause remains undetermined.

On Thursday “the focus was on locating and removing all victims, which was completed, and conducting interviews with witnesses. The next phase of the investigation will involve team analysis of witness statements, records, and the scene examination,’’ Ryan’s office said in the statement.

Ryan’s office said that there will be less visible activity at the scene this weekend, but stressed that the “fire investigation will continue to be active and on-going. ‘

The remains of all seven victims were removed from the building on Thursday and are expected to undergo autopsies at the state medical examiner's office, which is responsible for establishing cause of death and confirming the identity of the victims.

One issue that investigators are hoping to address is whether the fire alarms and smoke detectors inside the building functioned properly on Thursday. The building was last inspected in March 2013 and had working smoke and carbon monoxide detectors at the time, city officials said.

Today, Mayor Rodney M. Elliott said that about a week before the fatal fire -- he believes it was July 3 - the fire alarm system functioned properly. He said someone inside the building set off fireworks in a hallway, triggering an automatic alarm that brought Lowell firefighters to the building.

“There was a fire alarm system in there,’’ the mayor said. “Ti was activated and it fire department actually came to this location.’’

Elliott did not know if the system operated properly early Thursday morning when the fire was discovered by residents, a passing Lowell police officer and passersby.

Lowell fire spreads fast through apartments

Jennifer Mieth, spokeswoman for the state fire marshal, said the building had a hard-wired smoke alarm system, with detectors in each unit and in common areas.

The building did not have sprinklers and was not required to have them, officials have said.

Fire officials have pushed for legislation that would allow towns to require sprinklers in newly built single-family homes and duplexes, where most fire deaths occur, Mieth said. But the legislation has made no progress.

Because of the expense, there would be strong opposition to sprinkler requirements in old apartments, Mieth said.

All seven victims lived on the third floor, and a third floor resident who survived said today that the system did not work on her floor.

Standing near the burned-out Branch Street apartment Friday, Soth Sar, 43, said her third-floor apartment had a standard, round smoke detector in the kitchen, but not in other rooms. Her daughter, Savy Proeung, 13, said the hallway had another smoke alarm, a red, rectangular detector with a blinking light.

Sar said neither detector worked or was audible during the fire.

She said the building was not well-kept, with rat and roach problems as well as malfunctioning appliances, despite regular complaints to the landlord.

Some relatives of those lost in the fire continued their mourning today, including Bobby Christakos, the uncle of Tina Christakos, a 38-year-old woman who died in a third floor apartment along with a roommate, a man in his 70s.

“She had tons of energy,” the 54-year-old Christakos said in a telephone interview. “More than I did, and I ran five miles a day. One minute she’s here and the next she’s a mile down the road. She was a happy-go-lucky kid.”

He choked up thinking about his niece and the way she died.

“I’m going to miss my niece more than anything in the world, and her daughter’s going to miss her,” said Christakos, noting that Tina had a 20-year-old daughter. “Tina, you’re with mom and dad now. They’ll show you the light.”

Survivors today began the struggle of rebuilding their lives. The three-alarm fire essentially consumed the building and all their possessions, officials have said. The American Red Cross, along with the city of Lowell, is working to help them begin anew.

A relief fund was set up at the Jeanne D’Arc Credit Union.

The devastating fire has shocked the city and triggered the memories of some people whose own lives intersected with the building, including Phil Ramos, the son of the former owner, Carlos Ramos. The Ramos family sold the building to current owner Sanjay M. Patel in 2007, he said.

Phil Ramos said there were several fires in the building when his family owned it. At that time, he said, the smoke alarms worked.

“We looked out for that,” Phil Ramos said.

He was shocked when he learned of Thursday’s fire.

“I didn’t want to believe it was so bad,’’ he said. “We knew these people.’’

Phil Ramos called the current owner is a fastidious man.

“He’s the type that wants to dot the i’s and cross the t’s. I feel bad for him,” he said.

Ramos said he hopes part of the building is kept intact.

“I was hoping this was going to last forever,” he said. “It was like my second home.”

He said he’ll miss Torn Sak, known as Tony to most on Branch Street, which is a tight-knit community with a strong Cambodian presence.

“Tony and his family were amazing people. They taught me so much about life. He’s more of a family man than everyone else,” Phil Ramos said.

Nine people were taken to the hospital with assorted injuries, and more than 50 people were displaced. One firefighter suffered a leg injury, authorities said.

The building was last inspected in March 2013 and had working smoke and carbon monoxide detectors at the time, city officials said.

As the flames intensified, firefighters rescued at least five people from the third floor.

Thursday’s blaze was the deadliest fire in Massachusetts since 1994, when a wind-whipped fire killed seven residents in North Attleborough on Christmas Eve.